More particularly, this invention relates to a method in or relating to grinding of vegetable material in grinding apparatus which comprises discs mounted rotatably relative to one another in a casing and having an interspace between them, in which interspace the material to be ground is disintegrated during its passage in radially outward direction together with steam, from a central inlet. A superatmospheric pressure is maintained in said casing by means of the steam which together with the raw material, is introduced into the interspace between the grinding discs. Usually, an adjustable control valve is provided in an outlet from the casing for the ground product.